Semiconductor detectors with signal amplification by means of the avalanche effect are often used in radiation receivers for single photon detection.
On the one hand, constructions in use today require a mechanism to keep the field strength above the breakthrough field strength for purposes of single photon detection, the so-called Geiger mode. On the other hand, it should be possible after detection to decrease the breakthrough field so as to be able to detect rapidly following additional photons, so-called “quenching”.
There here exist passive strategies with resistors or semiconductor circuits located outside the semiconductor, and variants actively integrated into the semiconductor, which all have different advantages and disadvantages.
Efforts have been underway for several years to monolithically integrate this quenching (“quenching”). This offers both advantages with respect to the so-called fill factor, which describes the utilization of the semiconductor surface of the detector that faces the radiation, as well as time advantages, wherein dead times that cannot be used for detection purposes are diminished.
One of these solutions provides for a way to combine the avalanche effect and “quenching” into a monolithic structure. The main disadvantage to this solution is that rather low-resistance semiconductor layers must be used to ensure reliable function and find a suitable operating point. In addition, the geometric dimensions and layer thickness of the semiconductor substrate must be precisely adjusted, since the functional limitations associated with the low resistance here yield quite a narrow technological window. In the typical, unavoidable fluctuations in epitaxial layer thickness from the center to edge of a wafer, this leads to significant losses in yield.
In addition, the fact that a low-resistance substrate material was used directly implies a limitation of function to rather small pixel geometries. This essentially is because only small layer thicknesses can be depleted in low-resistance substrates, after which the breakthrough field strengths are reached rather quickly. The large capacities of the “floating” structures directly associated therewith greatly limit the potential swing required for function. This makes it harder to find a suitable operating point for such structures.
In addition, the limitation to very small pixels combined with the density required for the latter to ensure good quantum yield makes so-called “afterpulsing” into a major problem. In each microplasma of an avalanche process, the highly energy-laden, moving charge carriers cause individual radiating photons to spontaneously arise. These photons can radiate in all spatial directions within the semiconductor crystal. The composition of this radiation spectrum is such that these individual photons can radiate on average about 7 micrometers to 8 micrometers until being absorbed in the crystal. If only structures with a pixel geometry of up to roughly 4 micrometers can be realized with the low-resistance substrates, and the gap regions between two pixels are designed to be rather small, so as to achieve good quantum yield, triggering directly adjacent pixels becomes a major problem in such structures, since these kinds of phenomena disrupt the actual measurements. If the gap regions are enlarged, the quantum yield drops dramatically. This design dilemma is directly associated with the use of low-resistance semiconductor layers.
Document DE 690 11809 T2 discloses a semiconductor configuration with a semiconductor body having a first configuration area with a first conductivity type, which together with a second configuration area with a second conductivity type opposite the first, which is provided next to one of the main surfaces of the semiconductor body, forms a first pn-transition, which is reverse-biased in at least one operating mode of the configuration. An open additional region with the second conductivity type is provided, which is supplied within the first configuration area remotely from the main surfaces of the semiconductor body and spaced apart from the second configuration area, so that in one operating mode of the configuration, the depletion region of the first pn-transition reaches the open additional region prior to the breakthrough of the first pn-transition. The additional region forms another pn-transition with a highly doped separating region with a first conductivity type, which is supplied within the first configuration area between the open additional region and the second configuration area and spaced apart from the second configuration.
Known from Document DE 697 21 366 T2 are a diode as well as a converter circuit device. The diode is composed of a first semiconductor layer of a first conduction type, a second semiconductor layer of a second conduction type provided in the first semiconductor layer, a first main electrode electrically connected with the first semiconductor layer, as well as a second main electrode, which contacts the first semiconductor layer in a contact region within an edge portion of a transition area between the first and second semiconductor layer, wherein the edge portion lies on the edge of the second semiconductor region. The shortest lateral distance between the contact region and edge portion of the transition is not shorter than the diffusion length of minority charge carriers in the first semiconductor layer.